The production of phenol or phenol derivatives by catalytic partial oxidation of benzene or benzene derivatives is known. For example, the use of a variety of catalysts such as vanadium pentoxide on silica or zeolites (e.g. ZSM-5 and ZSM-11) at elevated temperatures has been disclosed in, for example, Iwamoto et al., J. Physical Chemistry (ACS), Vol. 87, No. 6, (1983) p. 903-905; Suzuki et al., 1988 Chemistry Letters of the Chemistry Society of Japan at pages 953-956; U.S. Pat. Nos. 5,001,280, 5,110,995, and 5,055,623, the disclosures of these publications being incorporated herein by reference.
Although useful for production of both phenol and phenol derivatives, the most significant potential utility of such processes is for the production of phenol in view of the commercial importance of that compound.
To date, practical commercial use of such processes has been hindered by low productivity, problems in controlling temperature rise of the highly exothermic reaction and resulting formation of undesired by-products, and the flammability of mixtures of nitrous oxide and benzene.
Recently processes of this type have been remarkably improved by the discovery that use of a molar deficiency of nitrous oxide (as opposed to the excess or at least stoichiometric quantities previously utilized) will increase selectivity to desired products, provide for higher conversion of nitrous oxide and higher catalyst production efficiency and can also allow for lower temperature rises resulting from the exothermic reaction and for operation with non-explosive mixtures. This discovery is described in detail in U.S. patent application Ser. No. 08/419371 filed Apr. 10, 1995 and copending herewith, the disclosure of said application being incorporated herein by reference.
However the use of large excesses of benzene beyond the amount required to optimize reaction selectivity requires the separation and recycle of large amounts of benzene. Even if benzene ratios are high enough to provide non-flammable mixtures in the reactor, the separation of benzene for recycle in downstream operations may leave flammable or explosive mixtures of benzene and nitrous oxide in downstream apparatus if nitrous oxide consumption in the reaction is less than 100%. Moreover, benzene is a flammable, toxic chemical and storage and handling of large excesses of that required for reaction increases the magnitude of potential leaks.
It is therefore recognized by those skilled in the art that techniques for limiting the excess of benzene to amounts dictated by productivity considerations and, simultaneously, achieving control of flammability and/or adiabatic temperature rise problems would represent a needed advance in the art.